The present invention relates to intrusion detection devices, and more particularly to a Fresnel lens grouping for an infrared sensor for mounting either on a wall or a ceiling.
Infrared sensors incorporating multiple Fresnel lens elements are known for use in detecting the presence of intruders in protected spaces. Some previous attempts to provide 360.degree. coverage for infrared radiation detection have relied on combinations of mirrors and Fresnel lenses, but this approach is undesirably expensive.
Mousavi U.S. Pat. No. 5,017,783 discloses a system based on a combination of Fresnel lenses and Fresnel prisms that is designed to provide a 360.degree. pattern of coverage when mounted, typically, on a ceiling.
Guscott U.S. Pat. No. 4,375,034 discloses using a combination of mirrors to produce a curtain of infrared detection for protecting a space from unwanted intrusion.
Guscott U.S. Pat. No. 4,707,604 discloses a ceiling mountable system based on mirrors that provides a plurality of radially outwardly extending generally vertical first curtains, a horizontal second generally disc-shaped pattern of sensitivity, and a conical downwardly directed third zone of sensitivity.
Muller et al. U.S. Pat. No. 4,990,783 also discloses use of mirrors to devise a curtain-like vertical zone of detection.
None of these infrared sensing devices, however, is capable of providing in a single reasonably inexpensive sensor device, at the option of the user, useful intrusion detection for a room either when mounted on a ceiling to provide 360.degree. coverage, or when mounted on a wall to provide wide-angle coverage or long-distance sensitivity.
What is still needed, then, is a single relatively inexpensive infrared sensing device for use in intrusion detection systems, mountable either on a wall or the ceiling, with the versatility for selectively providing horizontal fan-shaped zones of sensitivity, vertical curtains of sensitivity, all-around coverage, wide angle coverage, and long-range, narrow-field infrared detection coverage, all through the use of a single low-cost lens unit.